Issue 60

A. Bekhedda et alii, Frattura ed Integrità Strutturale, 60 (2022) 438-450; DOI: 10.3221/IGF-ESIS.60.30

-A load of 4 kg shall be applied to the test piece for 1 hour from t = 0h, we record deformation evolution with constant stress (it's creep phenomenon), the applied stress is located in the linear elastic domain [20]. After a time, t m = 1h, the applied stress σ 0 is removed, the recovery deformation is measured; A long time after removing the load, the deformation tends to a constant value, it is called permanent deformation.

Figure 6: Creep-recovery experience.

C REEP - RECOVERY BEHAVIOR

A

ccording to the graph above: The creep part: evolves in 3 phases: elastic, visco-elastic behavior and viscous flow behavior respectively. The first phase represents the instantaneous deformation ε EC due to the application of the load on the specimen, the second one is a parabolic curve with a significant slope in the primary minutes. The third phase is due to a flow dominated by the viscosity of the material. The slope of the curve is constant, but weaker than that of the previous phase until reaching the maximum strain ε Max . The recovery part: the prismatic test piece attempts to recover its initial form after the sudden load removal. This part evolves in 3 phases; the material takes an elastic behavior because of a reversible instantaneous deformation ε ER recorded immediately after unloading. Then it continues to recover a part of its viscoelastic deformation (Irreversible deformation ε Rev ) so that the material presents a viscoelastic behavior. In third phase, the material can’t longer recover its permanent or residual deformation recorded ε Res . The appearance was due to the uncompleted recovery of prismatic deformation. It has been noted:

 M1: Modified asphalt mixture (With ‘coarse’ waste PET size);  M2: Modified asphalt mixture (With ‘fine’ waste PET size);  O: Unmodified asphalt mixture (Without waste PET).

R ESULTS AND DISCUSSION

F

Temperature Effect ig. 7, shows the effect of temperature on the deformation evolution of a modified asphalt mixture as a function of time on low (0°C), medium (25°C), and high temperature (50°C) at different waste PET contents and waste PET sizes, and comparing it with an unmodified asphalt mixture.

443